This invention relates to a process for preparing polyurethane cast elastomers by chain extending an isocyanate prepolymer with aminocrotonate-terminated polyethers.
The casting of polyurethane elastomers in open molds is known. E.g., A. Awater, "PU cast elastomers" in Polyurethane Handbook, ed. G. Oertel (New York: Hanser Publishers, 1985), pages 372-388; J. H. Saunders and K. C. Frisch, "Urethane Elastomers" in Polyurethanes Chemistry and Technology (New York: Interscience Publishers, 1962), pages 273-314. Chain extenders used in the preparation of polyurethane cast elastomers include low molecular weight diamines (particularly aromatic diamines) and glycols (particularly 1,4-butanediol). Suitable hydroxyl-containing chain extenders also include low molecular weight polymeric diols such as polyether, polyester, polyacetal, polycarbonate, polyesterether, polythioether, polyamide, and polyesteramide diols (especially polyether and polyester diols). E.g., U.S. Pat. Nos. 5,079,327, 5,079,328, 5,081,204, and 5,081,210.
Aminocrotonate-terminated polyethers are known. E.g., U.S. Pat. Nos. 3,666,726, 5,066,824, 5,151,470, and 5,231,217. However, aminocrotonate-terminated polyethers have most typically been used for reaction injection molding, in which relatively rapid reaction of isocyanate components with isocyanate-reactive components is desired. E.g., U.S. Pat. No. 5,356,946 and application Ser. No. 07/699,592 (filed May 14, 1991) which is now U.S. Pat. No. 5,160,308. Such reactivities are not generally considered suitable for preparing cast elastomers in open molds. In addition, the use of low molecular weight aminocrotonate-terminated polyethers as chain extenders or crosslinkers has not been disclosed.
It was an object of the present invention to obtain cast elastomers based on aminocrotonate-terminated polyether chain extenders and/or crosslinkers having improved mechanical properties. It has been found that polyurethane elastomers prepared using aminocrotonate-terminated polyethers exhibit good tear strength, tensile strength, and elongation properties, along with excellent thermal properties.